The present invention relates to the field of electronic modules, and, more particularly, to electronic modules including fluid cooling systems.
Electronic devices are widely used in many types of electronic equipment. One electronic device is the integrated circuit which may include a silicon or gallium arsenide substrate and a number of active devices, such as transistors, etc. formed in an upper surface of the substrate. It is also typically required to support one or more such integrated circuits in a package that provides protection and permits external electrical connection.
As the density of active devices on typical integrated circuits has increased, dissipation of the heat generated has become increasingly more important. In particular, a relatively large amount of heat may be generated in multi-chip modules (MCMs), microwave transmitters, and photonic devices, for example.
A typical MCM may include a substrate upon which the electronic devices are mounted. Such substrates are generally made from a material that is suitable for withstanding the heat generated from the electronic devices. For example, ceramics such as low temperatures co-fired ceramics (LTCC) are commonly used for such substrates. Additionally, the MCM may also include a heat sink (e.g., fins) for dissipating heat from the electronic devices, and a fluid cooling circuit within the substrate for transferring heat between the electronic devices and the heat sink. That is, in two-phase cooling circuits, the heat from the electronic devices causes the cooling fluid to vaporize. Heat from the vapor is transferred to the heat sink, and the vapor then condenses to a liquid state. This liquid may then be re-circulated through the cooling circuit.
An example of such a substrate is disclosed in U.S. Pat. No. 5,870,823 to Bezama et al. entitled xe2x80x9cMethod of Forming a Multilayer Electronic Packaging Substrate with Internal Cooling Channels.xe2x80x9d The substrate includes a sintered ceramic body having cooling channels internal to and integral with the sintered ceramic body for the cooling a heat-generating electronic package placed on the sintered body. The flow of cooling fluid into and out of the cooling channels is controlled by manifolds and flow tubes connected to the substrate.
With the ever decreasing size of electronic devices and MCMs, it may be desirable to have fluid cooling circuits that do not require flow tubes, mechanical pumps, valves, etc., for circulating the cooling fluid therein. That is, such prior art devices may be relatively large and limit the ability to reduce the size of the substrate. In addition, such devices may be relatively expensive to produce.
In view of the foregoing background, it is therefore an object of the invention to provide an electronic module including a cooling substrate having a fluid cooling circuit therein for providing improved fluid flow control and associated methods.
This and other objects, features, and advantages in accordance with the present invention are provided by a method for making an electronic module including forming a cooling substrate having a fluid cooling circuit therein having a vertical passageway. The cooling substrate may be formed by forming a plurality of unsintered ceramic layers having passageways therein. The plurality of unsintered ceramic layers and the at least one resistive element may be assembled in stacked relation so that the passageways align to define the fluid cooling circuit and so that at least one resistive element extends in a cantilever fashion into the vertical passageway. Furthermore, the unsintered ceramic layers and the at least one resistive element may be heated to sinter and to cause the at least one resistive element to soften and deform downwardly adjacent vertical sidewall portions of the vertical passageway. The method may also include mounting at least one electronic device on the cooling substrate in thermal communication with the fluid cooling circuit.
More specifically, the at least one resistive element may be at least one layer of resistive ink.
Additionally, the at least one resistive element may include a plurality of resistive elements each between adjacent unsintered ceramic layers, and the plurality of resistive elements may be positioned adjacent opposing sidewalls of the vertical passageway.
The method may also include connecting the at least one resistive element to a voltage source for causing the at least one resistive element to heat and thereby facilitate fluid circulation in the cooling fluid circuit. The plurality of ceramic layers may be low temperature co-fired ceramic layers, for example. Also, a heat sink may be connected in thermal communication with the fluid cooling circuit.
An electronic module according to the invention includes a ceramic cooling substrate having a fluid cooling circuit therein having a vertical passageway defined by at least one vertical sidewall. The cooling substrate may include at least one resistive element on portions of the at least one vertical sidewall and extending into the at least one vertical sidewall a predetermined distance. Further, the electronic module may include at least one electronic device mounted on the cooling substrate and in thermal communication with the fluid cooling circuit.
More specifically, the at least one resistive element may include a plurality of resistive elements each extending into the at least one vertical sidewall the predetermined distance. For example, the predetermined distance may be greater than about 10 mils. Furthermore, the at least one vertical sidewall may include a plurality of sidewalls, and the plurality of resistive elements may be positioned adjacent at least two opposing vertical sidewalls of the vertical passageway. The ceramic substrate may include a low temperature co-fired ceramic, and the electronic module may further include a heat sink in thermal communication with the fluid cooling circuit.